Add option 'worker_shutdown'

Allow changing the default of 5000ms for shutdown time of each single
worker.

README.md

@@ -43,8 +43,10 @@ To start a new worker pool, you can either use `wpool:start_pool` (if you want t
 * **worker_type**: The type of the worker. The available values are `gen_server`. The default value is `gen_server`. Eventually we'll add `gen_statem` as well.
 * **worker**: The [`gen_server`](http://erldocs.com/current/stdlib/gen_server.html) module that each worker will run and the `InitArgs` to use on the corresponding `start_link` call used to initiate it. The default value for this setting is `{wpool_worker, undefined}`. That means that if you don't provide a worker implementation, the pool will be generated with this default one. [`wpool_worker`](https://hexdocs.pm/worker_pool/wpool_worker.html) is a module that implements a very simple RPC-like interface.
 * **worker_opt**: Options that will be passed to each `gen_server` worker. This are the same as described at `gen_server` documentation.
+* **worker_shutdown**: The `shutdown` option to be used in the child specs of the workers. Defaults to `5000`.
 * **strategy**: Not the worker selection strategy (discussed below) but the supervisor flags to be used in the supervisor over the individual workers (`wpool_process_sup`). Defaults to `{one_for_one, 5, 60}`
 * **pool_sup_intensity** and **pool_sup_period**: The intensity and period for the supervisor that manages the worker pool system (`wpool_pool`). The strategy of this supervisor must be `one_for_all` but the intensity and period may be changed from their defaults of `5` and `60`.
+* **pool_sup_shutdown**: The `shutdown` option to be used for the supervisor that manages the worker pool system (`wpool_pool`). Defaults to `brutal_kill`.
 * **queue_type**: Order in which requests will be stored and handled by workers. This option can take values `lifo` or `fifo`. Defaults to `fifo`.
 * **enable_callbacks**: A boolean value determining if `event_manager` should be started for callback modules.
   Defaults to `false`.

src/wpool_process_sup.erl

@@ -44,14 +44,15 @@ init({Name, Options}) ->
       %% We'll eventually add more types (like gen_statem),
       %% that's why this case remains
     end,
+  WorkerShutdown = proplists:get_value(worker_shutdown, Options, 5000),
   WorkerSpecs =
     [ { wpool_pool:worker_name(Name, I)
       , { WorkerType
         , start_link
         , [wpool_pool:worker_name(Name, I), Worker, InitArgs, Options]
         }
       , permanent
-      , 5000
+      , WorkerShutdown
       , worker
       , [Worker]
       } || I <- lists:seq(1, Workers)],

test/wpool_SUITE.erl

@@ -25,6 +25,7 @@
 -export([ stats/1
         , stop_pool/1
         , non_brutal_shutdown/1
+        , brutal_worker_shutdown/1
         , overrun/1
         , kill_on_overrun/1
         , too_much_overrun/1
@@ -39,8 +40,8 @@
 
 -spec all() -> [atom()].
 all() ->
-  [too_much_overrun, overrun, stop_pool, non_brutal_shutdown, stats,
-   default_strategy, default_options, complete_coverage, broadcast,
+  [too_much_overrun, overrun, stop_pool, non_brutal_shutdown, brutal_worker_shutdown,
+   stats, default_strategy, default_options, complete_coverage, broadcast,
    kill_on_overrun, worker_killed_stats].
 
 -spec init_per_suite(config()) -> config().
@@ -235,6 +236,25 @@ non_brutal_shutdown(_Config) ->
 
   {comment, []}.
 
+-spec brutal_worker_shutdown(config()) -> {comment, []}.
+brutal_worker_shutdown(_Config) ->
+  {ok, PoolPid} = wpool:start_sup_pool(wpool_SUITE_non_brutal_shutdown,
+                                       [{workers, 1},
+                                        {pool_sup_shutdown, 100},
+                                        {worker_shutdown, brutal_kill}]),
+  true = erlang:is_process_alive(PoolPid),
+  Stats = wpool:stats(wpool_SUITE_non_brutal_shutdown),
+  {workers, [{WorkerId, _}]} = lists:keyfind(workers, 1, Stats),
+  Worker = wpool_pool:worker_name(wpool_SUITE_non_brutal_shutdown, WorkerId),
+  monitor(process, Worker),
+  ok = wpool:stop_sup_pool(wpool_SUITE_non_brutal_shutdown),
+  receive {'DOWN', _, process, {Worker, _}, Reason} -> killed = Reason
+  after 200 ->
+          ct:fail(worker_not_stopped)
+  end,
+
+  {comment, []}.
+
 -spec stats(config()) -> {comment, []}.
 stats(_Config) ->
   Get = fun proplists:get_value/2,